The elucidation of CTL epitopes is crucial to the understanding of the molecular etiology of immune related disorders and the development of novel therapeutic strategies. Reliable identification of T-cell epitopes would, in particular, address an unmet need in the fields of cancer immunology, infectious disease, autoimmunity, and transplantation medicine. T-cell epitopes are short peptides displayed at the surface of antigen-presenting cells by the membrane-bound major histocompatibility complex (MHC) proteins, which are categorized as either class I or II. Class I molecules are expressed on the surface of nearly every cell of the body and present a sampling of short (8-14 residue) peptides derived from proteolytic turnover of proteins of both endogenous and exogenous origin. MHC class I found to be presenting epitopes recognized as ‘non-self’ are targets of direct attack from cytotoxic T-lymphocytes (CTLs).
The discovery of T-cell epitopes has proven to be a difficult endeavor given numerous characteristics of CTL antigen recognition including (a) extreme diversity of the T-cell repertoire generally ensures that clonotypes of interest are present in very low numbers, (b) T-cell epitope recognition is a low affinity interaction that must occur in the context of polygenic and highly polyallelic MHC molecules, (c) processing and presentation of both exogenous and endogenous peptides on MHC molecules makes for an enormous T-cell epitope space to be screened, and (d) substantial level of cross-reactivity is present in the T-cell repertoire, for example, it has been found that a single CTL is capable of recognizing on the order of 106 different peptide-MHC (pMHC) antigens. Extensive research and development efforts in the field of T-cell epitope discovery have been ongoing over the previous three decades but to date no practical high throughput method is available to routinely identify T-cell epitopes, Sharma and Holt, Human Immunology, 75: 514-519 (2014).
In view of the above, the availability of a high throughput and convenient method to routinely identify epitopes of selected T cells would be highly advantageous to many fields in medicine and biology, including cancer immunotherapy, vaccine development, organ transplantation, autoimmune disease diagnosis and therapy, and the like.